This invention relates to a modifier for high transparency, which can stably provide high transparency under wide ranges of processing conditions in injection molding, particularly when it is used by blending in methacrylic resins.
Because of their high transparency and excellent weather resistance, methacrylic resins are frequently used in various fields such as lightening apparatuses and outdoor products.
However, it is well known that the transparency of thermoplastic resins which are characterized by their transparency, particularly methacrylic resins, changes within considerable ranges depending on their processing conditions such as injection molding conditions. In addition, in view of the insufficient strength, addition of various impact resistance modifiers has been attempted for the purpose of improving their strength. For example, techniques that relate to the modification of their impact resistance are disclosed in JP-B-55-27576 (the term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d) and JP-A-62-230841 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). In that case, transparency of methacrylic resins is an essential condition to be maintained but is not sufficient condition from the practical point of view. It is therefore desirable to obtain moldings which can show high transparency and high quality stably under wide ranges of processing conditions.
However, when such resins are processed using the techniques so far disclosed, the just described requirement for obtaining moldings which can show high transparency and high quality stably under wide ranges of processing conditions cannot fully be satisfied. That is, moldings having high transparency can be obtained only within the range of narrow processing conditions, and the appearance of moldings becomes poor at the time of processing due to, for example, the aggregation of impact resistance modifiers. For example, when the molding temperature is increased with the aim of obtaining high transparency, thermal deterioration is apt to occur and burned marks are formed by only slight changes in the processing steps of the resin. On the other hand, when the injection molding temperature is set to a low level, the transparency is greatly spoiled. In other words, not only to simply ensure qualities of high transparency and high strength but also to obtain high transparency, high quality moldings stably within wide ranges of molding (processing conditions) are required as important factors in carrying out injection molding of methacrylic resins.
Though not related to the transparency as intended by the present invention, some attempts have been made to ensure moldings having stable high quality physical properties. For example, JP-B-1-29218 discloses a method in which the balance of strength and fluidity is improved by increasing fluidity using a methacrylic resin having a broad molecular weight distribution, and JP-B-2-2358 discloses a technique which uses a condition that an impact resistance modifier and a dispersing agent are blended in a latex form in order to avoid aggregation of the impact resistance modifier, as a means for reducing so-called fish eye at the time of extrusion molding.
However, these methods are different from the inventive idea of the present invention to narrow fluctuation range of transparency in injection molding under wide ranges of processing conditions.
In view of the above, it is an object of the present invention to provide a modifier which can modify impact resistance and provide high transparency products stably under broad processing conditions in injection molding, when it is used in methacrylic resins of which characteristic is transparency.
With the aim of developing a modifier which can add impact resistance-modifying effect to methacrylic resins without spoiling their transparency and also can keep the transparency of the object resin at a high level under wide ranges of molding conditions, the inventors of the present invention have conducted extensive studies and found that the aforementioned problems can be solved when an impact resistance modifier and a small amount of a polymer processability modifier are used in combination, thus resulting in accomplishment of the present invention.
Accordingly, the present invention relates to
(1) a methacrylic resin modifier, which comprises a blend of an impact resistance modifier and a polymer processability modifier that has a specific viscosity of from 2.5 to 5.0 when measured at a concentration of 0.4% by weight and at a temperature of 30xc2x0 C. using toluene as the solvent, wherein weight ratio of the impact resistance modifier and polymer processability modifier is from 95/5 to 80/20,
(2) the methacrylic resin modifier according to (1) above, wherein the impact resistance modifier is obtained by polymerizing monomer components comprising from 70 to 100% by weight (to be referred simply to as xe2x80x9c%xe2x80x9d hereinafter) of a (meth)acrylic ester, from 0 to 30% of an aromatic vinyl monomer and from 0 to 30% of other copolymerizable monomer (100% in total), in the presence of an acrylic rubber and/or a conjugated diene rubber, and
(3) the methacrylic resin modifier according to (1) or (2) above, wherein the polymer processability modifier is a polymer comprising from 50 to 70% of methyl methacrylate, from 1 to 50% of a (meth)acrylic acid alkyl ester, wherein the number of carbon atoms of the alkyl group is from 2 to 8, and from 0 to 30% of other copolymerizable monomer (100% in total).
The methacrylic resin modifier of the present invention is a modifier which comprises a blend of an impact resistance modifier and a particular polymer processability modifier and can be used in most of the commercially available methacrylic resins without particular limitation.
The aforementioned methacrylic resin is not particularly limited, but it may contain preferably 50% or more, more preferably 70% or more, of a methacrylic ester. Also, as the methacrylic ester, methyl methacrylate is desirable, so that a resin containing preferably 50% or more, more preferably 70% or more, of methyl methacrylate is more desirable.
The ratio of said impact resistance modifier and polymer processability modifier in the aforementioned methacrylic resin modifier, namely (impact resistance modifier)/(polymer processability modifier), is from 95/5 to 80/20, preferably from 95/5 to 90/10, as weight ratio. The ratio of the polymer processability modifier if too small would bear no sufficient effect to improve the aforementioned problems and if too large would produce no greater effect in spite of the high amount of the methacrylic resin modifier but rather reduce the impact resistance-improving effect and cause a tendency to reduce transparency of the methacrylic resin. It is considered that the reduction of transparency occurs due to relatively high molecular weight of the polymer processability modifier, which reduces its compatibility with the corresponding methacrylic resin.
The aforementioned impact resistance modifier is used for improving impact resistance and strength of the base material methacrylic resin, and any modifier conventionally used for methacrylic resins can be used without particular limitation.
A preferred example of the modifier conventionally used for methacrylic resins is an impact resistance modifier (I) which is obtained by polymerizing monomer components (to be referred also to as xe2x80x9cmonomer (M)xe2x80x9d hereinafter) comprising from 70 to 100%, preferably from 80 to 100%, of a (meth)acrylic ester, from 0 to 30%, preferably from 0 to 20%, of an aromatic vinyl monomer and from 0 to 30%, preferably from 0 to 15%, of other copolymerizable monomer (100% by weight in total), in the presence of an acrylic rubber and/or a conjugated diene rubber (to be referred also to as xe2x80x9crubber component (R)xe2x80x9d hereinafter).
The term xe2x80x9ca (meth)acrylic esterxe2x80x9d means an acrylic ester, a methacrylic ester, or a mixture thereof.
Amount of the monomer (M) is preferably from 20 to 65 parts by weight (to be referred to as xe2x80x9cpart(s)xe2x80x9d hereinafter), more preferably from 28 to 45 parts, based on 100 parts of the rubber component (R). The amount if larger than 65 parts would cause a tendency to reduce the strength-improving effect and if smaller than 20 parts would entail a difficulty in practically stably producing the modifier and also cause a tendency to reduce the strength-improving effect.
In this connection, when the (meth)acrylic ester in the monomer (M) which constitutes the impact resistance modifier (I) is less than 70%, it causes a tendency to reduce the strength-improving effect due to reduced compatibility. Also, when amount of the aromatic vinyl monomer exceeds 30%, it causes a tendency to reduce weather resistance.
Polymerization method of the impact resistance modifier (I) is not particularly limited, but a known emulsion polymerization is convenient from the practical point of view.
In this connection, the average particle size of the impact resistance modifier (I) in the latex of the rubber component (R) is preferably from 1,000 to 4,000 xc3x85, more preferably from 1,500 to 3,000 xc3x85, as a value measured by a light scattering method using a light source of 546 nm in wavelength. In addition, an acrylic rubber is desirable than a conjugated diene rubber from the viewpoint of weather resistance.
Examples of the aforementioned acrylic rubber include the compound produced in Example 1 which will be described later. They may be used alone or as a mixture of two or more.
Examples of the aforementioned conjugated diene rubber include those having an index of refraction adjusted by the copolymerization of a diene monomer with styrene. They may be used alone or as a mixture of two or more.
Examples of the aforementioned (meth)acrylic ester as a component of the monomer (M) include methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate and n-octyl acrylate. These compounds may be used alone or as a mixture of two or more.
Examples of the aforementioned aromatic vinyl monomer as a component of the monomer (M) include styrene and xcex1-methylstyrene. These compounds may be used alone or as a mixture of two or more.
Examples of the aforementioned other copolymerizable monomer include acrylonitrile. Such compounds may be used alone or as a mixture of two or more.
As the impact resistance modifier (I), various multi-layered structure substances are known, such as the multi-layered structure disclosed in JP-B-55-27576 and the modifier described in the examples which will be described later.
The aforementioned polymer processability modifier is used for further expanding the range of molding process conditions under which excellent transparency can be obtained.
It is necessary that the polymer processability modifier has a relatively large molecular weight, and a polymer having a molecular weight of from several times to several tens times (preferably from 10 times to 50 times) larger than that of the corresponding methacrylic resin (around 100,000 in weight average molecular weight) is generally effective. The molecular weight if similar to or lower than that of the corresponding methacrylic resin would bear no modifying effects of this invention. Also, the molecular weight if too large would cause large reduction of the transparency due to reduced compatibility with the matrix. Thus, the molecular weight is those showing a specific viscosity (xcex7sp) of from 2.5 to 5.0, preferably from 2.5 to 4.0.
In this case, the value xcex7sp is calculated by a formula xcex7sp=(xcex7xe2x88x92xcex70)/xcex70 using a viscosity xcex7 obtained by dissolving the aforementioned polymer processability modifier in toluene at a concentration of 0.4% and measuring the solution at a temperature of 30xc2x0 C. The value xcex70 is the viscosity of the solvent (toluene). When the polymer processability modifier having the aforementioned viscosity is added in a small amount, viscosity of the melting system at the time of molding is slightly increased, but it exerts an effect to reduce dependence of transparency on processing conditions. Though its technical reason is not clear, it is considered that transparency is stabilized by increased melt elasticity of the system.
The aforementioned polymer processability modifier is preferably a polymer comprising from 50 to 70%, preferably from 60 to 70%, of methyl methacrylate from the viewpoint of the compatibility with the matrix, from 1 to 50%, preferably from 30 to 40%, of a (meth)acrylic acid alkyl ester, wherein the number of carbon atoms of the alkyl group is from 2 to 8, which is preferably used as a soft component in view of not spoiling weather resistance of the methacrylic resin, and from 0 to 30% of other copolymerizable monomer (100% in total). When the amount of methyl methacrylate is too high, its compatibility with the matrix is reduced and transparency of the methacrylic resin tends to decrease, due to increased stiffness of the molecule in addition to its relatively large molecular weight. That is, it is desirable to copolymerize a soft component in addition to methyl methacrylate from the practical point of view. However, when the ratio of methyl methacrylate is too small, it causes a tendency to reduce the effect in further expanding the range of molding process conditions under which excellent transparency can be obtained. Also, when the amount of the (meth)acrylic acid alkyl ester, wherein the number of carbon atoms of the alkyl group is from 2 to 8, exceeds 50% or is less than 1%, it causes a tendency to reduce the effect in further expanding the range of molding process conditions under which excellent transparency can be obtained.
Examples of the (meth)acrylic acid alkyl ester, wherein the number of carbon atoms of the alkyl group is from 2 to 8, include butyl methacrylate, ethyl acrylate, butyl acrylate, octyl acrylate and 2-ethylhexyl acrylate, which are practical from the viewpoint, for example, of cost. These compounds may be used alone or as a mixture of two or more. Among these compounds, butyl methacrylate and butyl acrylate are particularly preferable.
Examples of the aforementioned other copolymerizable monomer include styrene, xcex1-methylstyrene and acrylonitrile. These compounds may be used alone or as a mixture of two or more.
The aforementioned polymer processability modifier can be produced by various polymerization methods known in the prior art, but an emulsion polymerization method is practical, because it is desirable that it has a relatively large molecular weight.
As a matter of course, the refractive index of this modifier must be adjusted to that of the methacrylic resin to be used as close as possible so that transparency of the obtained moldings is not spoiled.
As the aforementioned polymer processability modifier, commercially available products which can satisfy the aforementioned various conditions can be used (e.g., the polymer processability modifiers of KANE ACE PA series produced by Kaneka Corporation).
In this connection, the method for mixing the aforementioned impact resistance modifier and polymer processability modifier is not particularly limited, and it may be effected by blending powders of both modifiers and then blending the mixture with the methacrylic resin to be used or by blending the impact resistance modifier and polymer processability modifier, both obtained by polymerization, in the latex form, making the mixture into powder in the usual way and then blending the powder with a methacrylic resin.
Regarding the ratio of a methacrylic resin and the methacrylic resin modifier of the present invention, it is desirable that ratio of the methacrylic resin and methacrylic resin modifier, namely methacrylic resin/methacrylic resin modifier, is from 90/10 to 40/60, preferably from 85/15 to 50/50, as weight ratio.